Light shielding structure of a substrate for a liquid crystal device, liquid crystal device and projection type display device

a technology of liquid crystal devices and substrates, applied in static indicating devices, instruments, non-linear optics, etc., can solve problems such as leakage current to flow, leakage current generated by exposure of tft to stray light, and leakage current to aris

Inactive Publication Date: 2001-10-02
SEIKO EPSON CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

According to the substrate for a liquid crystal device, light impinging from above on the channel region and on the junctions between the channel region and the source / drain regions is shielded by the first shielding film, and light impinging from below is blocked by the second light shielding film. Through this arrangement, a leakage current which would otherwise be generated in the TFT exposed to light can be stably reduced.
According to the projection type display system, the projection type display system has a liquid crystal device of this invention, and prevents the entry of stray light through the first light shielding film on the substrate for the liquid crystal device, even when the back surface of the substrate for the liquid crystal device is exposed to such light as reflected from a dichroic prism or the like. Accordingly, even when light is intensified and such intensified light is incident on the liquid crystal device, it does not affect the TFT performance, and thus production of a projection type display system capable of reproducing bright, high quality images will be ensured.

Problems solved by technology

However, a leakage current caused by exposure of the TFT to stray light may arise as a result of light reflected from a polarizer placed on the back surface of the liquid crystal device, not to mention the adverse effects due to incident light itself.
If the light shielding film is placed on the back surface of the TFT such that it exceeds in size the opening of the black matrix placed on the opposite substrate, incident light strike: directly on the light shielding film, and light reflected therefrom illuminates the channel region of the TFT, which may cause it to generate a leakage current.
This is because, when a process necessary for the placement of a light shielding film on the back surface of the TFT is put into practice, precise alignment of a black matrix placed on the opposite matrix with a pixel region placed on the substrate for the liquid crystal device is difficult, and thus incident light through the opposite substrate directly impinges and is reflected on the part of light shielding film that exceeds in size the opening of the black matrix.
As a result, the channel region of TFT is illuminated, causing the leakage current to flow.
Particularly when alignment of the light shielding layer placed on the substrate for the liquid crystal device with the black matrix takes place with a large error, light reflected from the surface of light shielding film increases considerably, and, as the channel region is illumined by this reflective light, a leakage current from the TFT is increased, resulting in a degraded display as a result of flaws such as cross-talks or the like.
According to the substrate for the liquid crystal device, when the first light shielding film is formed in a floating state below the channel region of the TFT, irregular potential differences are generated between different terminals of the TFT, which may affect the TFT's performance.
This arrangement makes it unnecessary to prepare a layer only for light shielding.

Method used

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  • Light shielding structure of a substrate for a liquid crystal device, liquid crystal device and projection type display device
  • Light shielding structure of a substrate for a liquid crystal device, liquid crystal device and projection type display device
  • Light shielding structure of a substrate for a liquid crystal device, liquid crystal device and projection type display device

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Experimental program
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embodiment 1

(Embodiment 1)

FIGS. 1 and 2 represent the first preferred embodiment of a substrate for a liquid crystal device to which this invention has been applied. FIG. 1 is a plan view of pixels arrayed side by side, while FIG. 2 is a sectional view of the same along line A-A' of FIG. 1, that is, a cross-section of a semiconductor layer 1 which serves as an active layer of a TFT.

In FIG. 1. 1 represents a polysilicon film which forms a first layer of the semiconductor layer of the TFT, and, on the surface of semiconductor layer 1 is formed a gate insulating film 12 which has been produced by thermal oxidation, as shown in FIG. 2. Scan lines 2 act as common gate electrodes to TFTs arrayed in the same column (arrayed crosswise in the figure), 3 represents a data line which is so placed lengthwise as to intersect the scan line 2 at right angles, and is introduced to provide a voltage to the source regions of the TFTs arrayed in a vertical direction along the same row. The scan line 2 is made of ...

embodiment 2

In embodiment 2 like embodiment 1, the first light shielding film 7 is prepared smaller in size than a black matrix formed on an opposite substrate 31. Accordingly, incident light is prevented from impinging directly on the surface of first light shielding film 7, and thus generation of leakage current due to light reflected from the first light shielding film 7 can be effectively suppressed. Further, the first light shielding film 7 is so prepared as to have a smaller width than does the scan line 2, thereby preventing direct impingement of incident light on the first light shielding film 7 which extends below the scan line 2 in the same direction.

In embodiment 1, though not being restrictive, to effectively confer an extra capacitance to the drain of the TFT, the channel region 1c of the first layer of semiconductor layer 1 takes a course as indicated by symbol 1f: it extends above along the data line 3, and flexes towards an adjacent pixel electrode 14 (of the left adjacent pixel...

embodiment 3

can also be produced through the same production processes as used for the production of embodiment 1.

(Embodiment 4)

FIGS. 9 and 10 represent the fourth preferred embodiment of a substrate for liquid crystal device to which this invention has been applied. FIG. 9 is a plan view of pixels arrayed side by side, while FIG. 10 is a sectional view of the same along line D-D' of FIG. 9, that is, a cross-section of a semiconductor layer 1 which serves as an active layer of the TFT. Embodiment 4 differs from embodiment 3 in that a scan line 2 has a laminated structure consisting of a polysilicon layer 2a and a metal film such as a tungsten film, a molybdenum film, etc., or a metal alloy film 2b, and in that the first light shielding film 7 (areas shaded with parallel lines having a positive gradient) is place only below a data line 3 (second light shielding film). In embodiment 3 described above, as a polysilicon film constituting the scan line 2 alone is present above the first light shield...

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Abstract

Placement of a first light shielding film at least below the channel region of a TFT which drives a pixel, and of a second light shielding film above the same prevents impingement of light coming from above or from below on that channel region. Further, a second light shielding film is formed to cover the channel region and the first light shielding film, thereby to prevent the surface of the first light shielding film from direct exposure to light.

Description

1. Field of the InventionThis invention relates to a technique which is suitably adapted for production of a substrate for a liquid crystal device, and a liquid crystal device and projection type display device based on the use thereof This invention relates more particularly to a light shielding structure of the substrate for the liquid crystal device which is used as a pixel switching element of a thin film transistor (to be abbreviated as TFT hereinafter).2. Description of Related ArtConventionally, a liquid crystal device is put into practice where pixel electrodes have been arranged in the form of a matrix on a glass substrate, and TFTs made of an amorphous silicon film or a polysilicon film have been prepared in correspondence with each pixel electrode, and which is so constructed as to drive a liquid crystal by applying a voltage through the TFT to each pixel electrode.Among such liquid crystal devices, one incorporating a polysilicon film of which it is possible to assemble ...

Claims

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Application Information

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Patent Type & Authority Patents(United States)
IPC IPC(8): G02F1/13G02F1/1362
CPCG02F1/136209G02F1/136
Inventor MURADE, MASAO
Owner SEIKO EPSON CORP
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